Recent anthrax-related bioterrorism incidents highlight the need for effective antimicrobial agents for treatment and prevention. Penicillin antibiotics has been historically the first choice for this purpose. However, concerns for drug resistance have resulted in recommendations that these drugs no longer be considered as drug of choice. This application proposes to define the biochemical and molecular basis of resistance to beta-lactams, as well as the potential for resistance to emerge in B. anthracis. The aims of the proposed experiments are: 1) to determine whether one or both of the two putative B-lactamase genes code for a B-lactamase and 2) to identify regulatory genes controlling B lactamase gene expression. Specifically, individual Beta-lactamase gene will be cloned and expressed. Encoded protein will be purified and in vitro biochemical studies will be performed to determine its substrate profile and inhibitor specificity. Candidate regulatory genes as identified by genome scanning will be cloned and their sequence will be determined. Mutants of regulatory genes will be constructed using genetic manipulation to assess the function of each gene product. The result of this study will elucidate the molecular mechanism underlying the resistance of Bacillus anthracis to penicillin antibiotics and inform decisions about the clinical utility of Beta-lactam antibiotics.